In photolithography used in manufacturing a semiconductor device etc., a difference occurs in the dimensions of a pattern on completion due to a difference in exposure conditions, even between exposures using the same mask pattern. The relationship between the exposure amount and the pattern dimensions is found beforehand, and an appropriate exposure amount at which desired pattern dimensions are obtained is determined when exposure is performed, for example. The robustness of the pattern dimensions against the change in exposure conditions is called an exposure tolerance. In photolithography, it is important to estimate the exposure tolerance with high reliability.